1. Field of the Invention
The invention relates to a sensing membrane from a semiconductor fabricating process and a micro-electro-mechanical system device using the same.
2. Description of the Related Art
Consumer electronic products are getting more and more popular in the market recently. Various electronic products have increasingly gained their visibility in modern people's daily life. Along with the trend for multifunctional and compact-sized products, manufacturers are devoting in developing products of better integration and lower costs. Over the last few years, manufacturers have integrated Micro-Electro-Mechanical System (MEMS) devices into various products to reduce the size of the products. Common examples of such MEMS devices include MEMS microphones and G-sensors.
Of all the different types of MEMS devices, a kind of sensing device transduces an external signal into an electric signal through the vibration of a membrane. The vibration is generated as the membrane receives the external signal. As a result, many types of signals can be detected by the sensing device accordingly. The sensitivity of the membrane to vibrate with the external signals is vital to the sensing property of the device. However, vast membrane residual stress is accumulated in the membrane structure during subjecting to the manufacturing process, particularly when the membrane is made of complex materials of different coefficients of expansion. The membrane residual stress not only affects the sensitivity of the membrane but also lowers the quality of the sensing device.
On the other hand, the widely applied MEMS devices in the industry are usually made through a wafer-level process, in which several MEMS elements are formed on a single wafer. After the MEMS elements are formed, following process steps including a sawing process are performed to form a single MEMS device. Because the vibration frequency of the membrane is related to the area of the membrane, it is difficult to change the area of the membrane when the desired vibration frequency and the membrane thickness are predetermined. These limitations must be taken into account while determining the volume of the device and the numbers of MEMS element forming on each unit area of the wafer.